JP2021059834A - Carbon fiber precursor acrylic fiber, carbon fiber, and production method of the same - Google Patents

Abstract

To provide a carbon fiber enabling high intensity of a CFRP-made tank by minimizing variation in fiber volume content of CFRP by curbing generation of an air bubble, minimizing variation in resin content, and suppressing a void inside the CFRP of the CFRP-made tank when impregnating a carbon fiber bundle with thermoset resin in a process of producing the CFRP-made tank by a filament binding method.SOLUTION: A carbon fiber according to a first embodiment of this invention has center line average roughness Ra of a monofilament surface of 6.0 nm or larger and 13 nm or smaller and a long axis/short axis ratio of a monofilament of 1.11 or larger and 1.245 or smaller. The carbon fiber according to the first embodiment can be obtained by subjecting a carbon fiber precursor acrylic fiber according to a second embodiment to flame-resistance processing and carbonization in a specified condition, the carbon fiber precursor acrylic fiber having center average roughness Ra of a monofilament surface of 18 nm or larger and 27 nm or smaller and a long axis/short axis ratio of a monofilament of 1.11 or larger and 1.245 or smaller.SELECTED DRAWING: Figure 3

Description

The present invention relates to carbon fiber precursor acrylic fibers, carbon fibers and methods for producing them.

In recent years, the range of use of pressure vessels used for various purposes in various industries has been expanding more and more, such as pressure vessels (CNG tanks) mounted on automobiles that use natural gas as fuel and fuel cells that use hydrogen gas as fuel. It is also being deployed in pressure vessels (CHG tanks) mounted on vehicles. The market is required to reduce the weight of pressure vessels for automobiles in order to improve fuel efficiency.

A pressure vessel using carbon fibers is usually made of a metal or resin called a liner by impregnating a bundle of carbon fiber single fibers (hereinafter, sometimes referred to as a carbon fiber bundle) with a resin such as epoxy resin. It is obtained by subjecting the resin to a cylindrical object of No. 1 and heat-curing the resin. (Hereinafter, it may be called the filament winding method.)
Carbon fibers are generally known to have high specific strength and specific elastic modulus, and a pressure vessel using carbon fibers (hereinafter, may be referred to as a CFRP tank) is a metal pressure vessel. It is lightweight while having the same strength.
However, pressure vessels for automobiles are required to have higher strength, especially in the field of CHG tanks.
In order to increase the strength of the CFRP tank, in addition to increasing the strand strength of the carbon fiber used, voids are generated in the carbon fiber reinforced plastic (hereinafter, may be referred to as CFRP) constituting the CFRP tank. It is important to suppress and reduce the unevenness of the fiber volume content in CFRP.

In carbon fibers manufactured by the conventional technique, the shallower the wrinkles formed on the surface of the single fibers constituting the carbon fiber bundle, the higher the cohesiveness of the carbon fiber bundle, and the impregnation of the carbon fiber bundle with the resin. It became insufficient and tended to form voids in CFRP. On the contrary, if the wrinkles formed on the surface of the single fiber are too deep, the focusing property of the carbon fiber bundle becomes insufficient, the impregnation of the resin is not constant, and the unevenness of the fiber volume content in CFRP becomes large. There was a tendency to end up.
Further, as the cross-sectional shape of the single fibers constituting the carbon fiber bundle approaches a perfect circle, the gap between the single fibers becomes smaller, the impregnation of the carbon fiber bundle with the resin becomes insufficient, and voids are formed in the CFRP. There was a tendency to end up. On the contrary, as the cross-sectional shape of the single fiber in the fiber axis direction becomes farther from the perfect circle, the variation of the gap between the single fibers becomes large, the impregnation of the resin into the carbon fiber bundle becomes not constant, and the fiber volume in CFRP. The content rate spots tended to grow larger.
Therefore, in order to achieve high strength of the CFRP tank, carbon fibers having high strand strength and appropriately controlled wrinkles formed on the cross-sectional shape of the single fiber and the surface of the single fiber are desired. ing.

In Patent Document 1, by controlling the surface uneven structure of the surface of the single fiber constituting the carbon fiber bundle, while maintaining the interfacial adhesiveness with the resin, the decrease in fracture toughness due to stress concentration is suppressed, and the carbon fiber is also used. It is described that by making the cross-sectional shape of the single fibers constituting the bundle closer to a perfect circle, a carbon fiber reinforced composite material having high mechanical properties can be obtained by suppressing a decrease in fracture toughness due to stress concentration. However, since the cross-sectional shape of the single fibers constituting the carbon fiber bundle is close to a perfect circle and the surface irregularities of the single fibers are shallow, the obtained CFRP tank may have many voids, which is high when there are many voids. It is difficult to obtain strength.

Further, in Patent Document 2, the width of the carbon fiber bundle is made into a uniform flat shape, and the width fluctuation of the fiber bundle after resin impregnation is suppressed, so that the carbon fiber bundle suitable for manufacturing a CFRP tank by the filament winding method is suitable. Is stated to be obtained. Therefore, the cross-sectional shape and the arithmetic mean roughness of the surface of the single fibers constituting the carbon fiber bundle are controlled. However, since the cross-sectional shape of the single fibers that make up the carbon fiber bundle used is close to a perfect circle, it is easy for the single fibers to be packed closely together, and the obtained CFRP tank tends to have many voids, which is high. It is difficult to obtain strength.

Japanese Unexamined Patent Publication No. 2010-285710 Japanese Unexamined Patent Publication No. 2012-154000

The present invention has been made to solve such a problem, and is a filament winding method by appropriately controlling the cross-sectional shape of the single fibers constituting the carbon fiber bundle and the wrinkles formed on the surface of the single fibers. When the carbon fiber bundle is impregnated with the heat-curable resin in the process of manufacturing the CFRP tank, the formation of air bubbles can be suppressed, the unevenness of the resin content can be reduced, and the void inside the CFRP of the CFRP tank can be reduced. Carbon fibers and carbon fiber bundles that can be suppressed to reduce the unevenness of the fiber volume content of CFRP and increase the strength of CFRP tanks, and carbon fiber precursors that are the raw materials for the carbon fibers and carbon fiber bundles. It is an object of the present invention to provide an acrylic fiber and a carbon fiber precursor acrylic fiber bundle, and a method for producing the carbon fiber precursor acrylic fiber bundle and the carbon fiber bundle.

The purpose is solved by the following method.
That is, in the first aspect of the present invention, the center line average roughness Ra of the surface of the single fiber is 6.0 nm or more and 13 nm or less, and the major axis / minor axis of the single fiber is 1.11 or more and 1.245 or less. It is a fiber.
The carbon fiber according to the first aspect of the present invention preferably has one or more of the following configurations [1] to [3].
[1] The dent distance / minor axis of the single fiber is 0.011 or more and 0.018 or less.
[2] The center line average roughness Ra of the surface of the single fiber is 10 nm or less, and the major axis / minor axis of the single fiber is 1.135 or more.
[3] The recess distance / minor axis of the single fiber is 0.0145 or more.

In the second aspect of the present invention, the carbon fiber precursor acrylic having a centerline average roughness Ra of the surface of the single fiber of 18 nm or more and 27 nm or less and the major axis / minor axis of the single fiber of 1.11 or more and 1.245 or less. It is a fiber.
The carbon fiber precursor acrylic fiber according to the second aspect of the present invention preferably has one or more of the following configurations [4] to [6].
[4] The dent distance / minor axis of the single fiber is 0.011 or more and 0.018 or less.
[5] The center line average roughness Ra of the surface of the single fiber is 24 nm or less, and the major axis / minor axis of the single fiber is 1.135 or more.
[6] The recess distance / minor axis of the single fiber is 0.0145 or more.

A third aspect of the present invention is a method for producing a carbon fiber precursor acrylic fiber bundle, which comprises the following steps 1) to 3) and satisfies the following conditions 4) and 5).
1) Acrylonitrile-based polymer solution is discharged from a spinneret to coagulate in a coagulation liquid having a coagulation liquid concentration of 65% by mass or more and 70% by mass or less and a coagulation liquid temperature of 36 ° C. or more and 40 ° C. or less. A step of obtaining a yarn and at the same time taking it while controlling the tension applied to the coagulated yarn to 55 mgf / filament or more and 75 mgf / filament or less.
2) After the coagulated yarn taken in the above 1) step is drawn in the air at 1.00 times or more and 1.15 times or less, using water at 50 ° C. or higher, from 4 steps or more and 7 steps or less. Stretching / washing is performed in a magnification range of 2.4 times or more and 2.7 times or less in a washing / stretching tank, and 0.97 times or more and 1.1 times or less in a hot water tank using water at 95 ° C. or higher. A step of obtaining a drawn yarn by relaxing or drawing the above.
3) A step of applying an oil agent to the drawn yarn obtained in the above 2) step, drying it, and then stretching it to 3.0 times or more and 4.5 times or less in a pressurized steam atmosphere of 130 ° C. or higher and 160 ° C. or lower.
4) The total draw ratio of the coagulated yarn from the time when the coagulated yarn in the step 1) is taken up to the time when the drawn yarn in the step 2) is obtained is 2.4 times or more and 2.7 times or less.
5) The total draw ratio from the taking of the coagulated yarn in the step 1) to the drawing in the pressurized steam atmosphere of the step 3) is 9.0 times or more and 12 times or less.

A fourth aspect of the present invention is a method for producing a carbon fiber bundle, which comprises the following steps 4) to 6).
4) The flame-resistant carbon fiber precursor acrylic fiber bundle composed of the carbon fiber precursor acrylic fiber of the second aspect of the present invention is heated to 200 ° C. or higher and 300 ° C. or lower in an oxidizing atmosphere to form a flame-resistant fiber bundle. Chemical process.
5) A pre-carbonization step in which the flame-resistant fiber bundle is heated at 550 ° C. or higher and 800 ° C. or lower in a non-oxidizing atmosphere to form a pre-carbonized fiber bundle.
6) A high-temperature carbonization step in which the pre-carbonized fiber bundle is heated at 1200 ° C. or higher and 3000 ° C. or lower in a non-oxidizing atmosphere to form a carbon fiber bundle.

By appropriately controlling the cross-sectional shape of the single fiber of carbon fiber and the wrinkles formed on the surface of the single fiber according to the present invention, the heat-curable resin is carbonized in the process of manufacturing a CFRP tank by the filament winding method. When impregnated into a fiber bundle, the formation of air bubbles can be suppressed, the unevenness of the fiber content can be reduced, and as a result, the strength of the CFRP tank can be increased. And the carbon fiber is provided.

FIG. 1 is a schematic diagram for explaining the definitions of the major axis and the minor axis of a single fiber. FIG. 2 is a schematic diagram for explaining the definition of the recessed distance of the single fiber. FIG. 3 is an electron micrograph of a cross section of a single fiber constituting the carbon fiber precursor acrylic fiber bundle of Example 2. FIG. 4 is an electron micrograph of a cross section of a single fiber constituting the carbon fiber precursor acrylic fiber bundle of Comparative Example 9. FIG. 5 is an electron micrograph of a cross section of the carbon fiber precursor acrylic fiber of Comparative Example 7.

The carbon fiber precursor acrylic fiber of the present invention has a center line average roughness Ra of the surface of a single fiber of 18 nm or more and 27 nm or less.
In the present invention, by setting the centerline average roughness Ra of the surface of the single fiber of the carbon fiber precursor acrylic fiber to 18 nm or more, a carbon fiber bundle made of the single fiber of the carbon fiber obtained from the carbon fiber precursor acrylic fiber can be obtained. It is possible to suppress excessive focusing, and it becomes easy to impregnate the carbon fiber bundle with the resin. Further, by setting the centerline average roughness Ra of the surface of the single fiber of the carbon fiber precursor acrylic fiber to 27 nm or less, the bundling property of the carbon fiber bundle made of the single fiber of the carbon fiber obtained from the carbon fiber precursor acrylic fiber is set. Can be prevented from being insufficient, and the carbon fiber bundle can be easily impregnated with the resin uniformly.
From the viewpoint of increasing the strength of the CFRP tank, it is more preferable that the center line average roughness Ra of the single fiber surface of the carbon fiber precursor acrylic fiber is 24 nm or less. The center line average roughness Ra of the surface of the single fiber of the carbon fiber precursor acrylic fiber can be measured by the method described in Examples.

The carbon fiber precursor acrylic fiber of the present invention has a single fiber with a major axis / minor axis of 1.11 or more and 1.245 or less. In the present invention, by setting the major axis / minor axis of the single fiber of the carbon fiber precursor acrylic fiber to 1.11 or more, the bundle of the single fiber of the carbon fiber precursor acrylic fiber (hereinafter, referred to as the carbon fiber precursor acrylic fiber bundle). It becomes possible to sufficiently secure a gap between the single fibers constituting the carbon fiber bundle obtained by making the carbon fiber bundle flame-resistant and carbonizing the carbon fiber bundle, and it becomes easy to impregnate the carbon fiber bundle with the resin. Further, by setting the major axis / minor axis of the single fiber of the carbon fiber precursor acrylic fiber to 1.245 or less, it is possible to prevent the gap between the single fibers of the carbon fiber obtained by flame resistance and carbonization from becoming excessive, and to prevent carbon. It becomes easy to uniformly impregnate the fiber bundle with the resin.
From the viewpoint of increasing the strength of the CFRP tank, it is more preferable that the major axis / minor axis of the single fiber of the carbon fiber precursor acrylic fiber is 1.135 or more.
The major axis / minor axis of the single fiber of the carbon fiber precursor acrylic fiber is the smallest area of the rectangle circumscribing with respect to the cross section 1 perpendicular to the fiber axis direction of each single fiber constituting the carbon fiber precursor acrylic fiber. It is the average value of the ratio (X / Y) of the length X of the long side and the length Y of the short side of the rectangle 2. Specifically, it can be measured by the method described in Examples (see FIG. 1).

The carbon fiber precursor acrylic fiber of the present invention preferably has a single fiber recess distance / minor axis of 0.011 or more and 0.018 or less.
In the present invention, by setting the recess distance / minor axis of the single fibers of the carbon fiber precursor acrylic fiber to 0.011 or more, a sufficient gap between the single fibers of the carbon fibers obtained from the carbon fiber precursor acrylic fiber is sufficiently secured. It becomes possible to impregnate the carbon fiber bundle with the resin. Further, by setting the recess distance / minor axis of the single fiber of the carbon fiber precursor acrylic fiber to 0.018 or less, the gap between the single fibers of the carbon fiber obtained from the carbon fiber precursor acrylic fiber becomes excessive. This prevents the carbon fiber bundles from being uniformly impregnated with the resin.
From the viewpoint of increasing the strength of the CFRP tank, it is more preferable that the recess distance / minor axis of the single fiber of the carbon fiber precursor acrylic fiber is 0.0145 or more.
The dent / minor axis of the single fiber of the carbon fiber precursor acrylic fiber is the smallest area of the rectangle circumscribing with respect to the cross section 1 perpendicular to the fiber axis direction of each single fiber constituting the carbon fiber precursor acrylic fiber. It is an average value of the inverse ratio (Z / Y) of the length Y of the short side of the rectangle (see FIG. 1) and the recessed distance Z defined as follows for the same cross section 1. Specifically, it can be measured by the method described in Examples.
The dent distance is the area of the space (dent) surrounded by the straight line 3 which is in contact with the cross section 1 perpendicular to the fiber axis direction of each single fiber constituting the carbon fiber precursor acrylic fiber at two points and the cross section 1 of the fiber. Is the maximum depth of the dent, and is defined as the distance Z between the point 4 farthest from the straight line 3 and the straight line 3 among the points on the circumference of the cross section 1 surrounding the dent (see FIG. 2).

The carbon fiber precursor acrylic fiber of the present invention is obtained by spinning an acrylonitrile-based polymer solution in which an acrylonitrile-based polymer is dissolved in a solvent.
The acrylonitrile-based polymer used in the present invention is a polymer obtained by polymerizing acrylonitrile as a main monomer. The acrylonitrile-based polymer may be a homopolymer obtained only from acrylonitrile, or a copolymer obtained by copolymerizing other monomers in addition to acrylonitrile as a main component.

The content of the acrylonitrile unit in the acrylonitrile-based polymer can be determined in consideration of the quality required for the obtained carbon fiber bundle, and is, for example, 90% by mass or more and preferably 99.5% by mass or less, preferably 96% by mass. It is more preferably 99.5% by mass or less. When the content of the acrylonitrile unit is 90% by mass or more, the single fibers are not fused to each other in each of the flame resistance and carbonization steps for converting the carbon fiber precursor acrylic fiber into carbon fiber. , It is possible to prevent a decrease in the strand strength of the carbon fiber bundle. Further, in a treatment such as stretching with a heating roller or pressurized steam, adhesion between single fibers can be avoided. When the content of the acrylonitrile unit is 99.5% by mass or less, the solubility in the solvent does not decrease and the precipitation and solidification of the acrylonitrile-based polymer can be prevented, so that the carbon fiber precursor acrylic fiber can be stably produced. it can.

As the monomer unit other than acrylonitrile in the acrylonitrile-based polymer, a vinyl-based monomer copolymerizable with acrylonitrile can be appropriately selected, and a vinyl-based single amount that improves the hydrophilicity of the acrylonitrile-based polymer. A vinyl-based monomer that promotes the body and flame resistance reaction is preferable.
The method for synthesizing the acrylonitrile-based polymer may be any polymerization method, and the present invention is not limited by the difference in the polymerization method.

Examples of the solvent for the acrylonitrile polymer solution include organic solvents such as dimethylacetamide, dimethyl sulfoxide and dimethylformamide, and aqueous solutions of inorganic compounds such as zinc chloride and sodium thiocyanate. Of these, dimethylacetamide, dimethyl sulfoxide, and dimethylformamide are preferable because they have high dissolving power in acrylonitrile-based polymers.

The polymer concentration of the acrylonitrile-based polymer solution is preferably 20% by mass or more and 25% by mass or less. More preferably, it is 21% by mass or more and 24% by mass or less. By setting the polymer concentration to 20% by mass or more, the voids inside the coagulated yarn are reduced, so that the strand strength of the carbon fiber bundle can be increased. Further, when the polymer concentration is 25% by mass or less, the acrylonitrile-based polymer solution can maintain an appropriate viscosity and fluidity, so that the carbon fiber precursor acrylic fiber can be easily produced.

Examples of the spinning method for obtaining the carbon fiber precursor acrylic fiber include a wet spinning method in which an acrylonitrile-based polymer solution is spun directly into a coagulating liquid and coagulated when it is discharged from a spinneret (hereinafter referred to as a nozzle), in the air. There are a dry spinning method of spinning and solidifying in the air, a dry and wet spinning method of spinning in the air and then solidifying in a coagulating liquid.
In the present invention, an aqueous organic solvent solution having an organic solvent concentration of 65% by mass or more and 70% by mass or less and a temperature of 33 ° C. or more and 40 ° C. or less is used as a coagulating liquid, and an acrylonitrile-based polymer solution of 3000 or more is preferably contained in the coagulating liquid. It is preferable to obtain a coagulated yarn by discharging from a nozzle having a discharge hole of 12,000 or more, more preferably 24,000 or more, and solidifying the mixture. The number of discharge holes contained in one nozzle is preferably 120,000 or less, more preferably 60,000 or less.

By setting the concentration of the organic solvent (also referred to as the coagulation liquid concentration) of the organic solvent aqueous solution which is the coagulation liquid to 65% by mass or more, the major axis / minor axis of the single fiber of the carbon fiber precursor acrylic fiber and the center line of the single fiber surface It is possible to prevent the average roughness Ra from becoming too large. Further, by setting the concentration of the organic solvent aqueous solution in the coagulating liquid to 70% by mass or less, the major axis / minor axis of the obtained single fiber of the carbon fiber precursor acrylic fiber and the center line average roughness Ra of the single fiber surface are small. It becomes possible to prevent it from becoming too much. In order to control the major axis / minor axis of the single fiber of the carbon fiber precursor acrylic fiber and the centerline average roughness Ra of the single fiber surface of the carbon fiber precursor acrylic fiber, the concentration of the organic solvent in the organic solvent aqueous solution which is the coagulation liquid is adjusted. It is more preferably 66% by mass or more and 68% by mass or less.
By setting the temperature of the organic solvent aqueous solution as the coagulating liquid to 33 ° C. or higher, the major axis / minor axis of the obtained single fiber of the carbon fiber precursor acrylic fiber and the center line average roughness Ra of the single fiber surface become too large. Can be prevented. Further, by setting the temperature of the organic solvent aqueous solution of the coagulation liquid to 40 ° C. or lower, the major axis / minor axis of the obtained single fiber of the carbon fiber precursor acrylic fiber and the center line average roughness Ra of the single fiber surface become too small. It becomes possible to prevent that. In order to control the major axis / minor axis of the single fiber of the carbon fiber precursor acrylic fiber and the center line average roughness Ra of the surface of the single fiber, the temperature of the organic solvent aqueous solution as the coagulation liquid may be 36 ° C. or higher and 40 ° C. or lower. It is preferably 36 ° C. or higher and 39 ° C. or lower, more preferably.

In the present invention, it is preferable that the tension applied to the coagulated yarn (referred to as take-up tension) when the coagulated yarn is taken up from the coagulating liquid is 55 mgf / filament or more and 75 mgf / filament or less. The method for measuring the take-up tension is the same as the measuring method described in the examples.
By setting the take-up tension when the coagulated yarn is taken up from the coagulating liquid to 55 mgf / filament or more, it is possible to prevent the coagulated yarn from being scattered in the coagulating liquid and causing poor take-up. In addition, it is possible to prevent the major axis / minor axis of the obtained carbon fiber precursor acrylic fiber single fiber and the center line average roughness Ra of the single fiber surface from becoming too small.
Further, by setting the take-up tension when taking up the coagulated yarn from the coagulating liquid to 75 mgf / filament or less, the major axis / minor axis of the single fiber of the carbon fiber precursor acrylic fiber obtained and the average roughness Ra of the center line of the surface of the single fiber are Ra. Can be prevented from becoming too large.

The coagulated yarn is taken from the coagulating liquid from the viewpoint of controlling the major axis / minor axis of the single fiber of the carbon fiber precursor acrylic fiber and the center line average roughness Ra of the single fiber surface and the production stability of the carbon fiber precursor acrylic fiber bundle. It is more preferable that the take-up tension is 57 fmg / filament or more and 71 mgf / filament or less.

The collected coagulated yarn may be stretched in the air while containing the coagulating liquid. The stretching ratio in the air is preferably 1.00 times or more and 1.15 times or less. Excessive stretching can be suppressed by setting the stretching ratio to 1.15 times or less. From the viewpoint of increasing the strand strength of the carbon fiber bundle and improving the performance of the CFRP tank, it is more preferable that the draw ratio is 1 time or more and 1.05 times or less.

In the present invention, the coagulated yarn is stretched in the air and then washed and stretched. The cleaning method may be any method as long as the solvent can be removed. For example, washing / stretching is performed in a multi-stage washing / stretching tank set to a temperature in the range of 50 ° C. or higher and lower than 100 ° C. Here, the number of stages of the washing / stretching tank is not particularly limited, but about 3 stages or more and 10 stages or less is appropriate. It is preferably 4 steps or more and 7 steps or less. The draw ratio is preferably 2.4 times or more and 2.8 times or less.
By setting the draw ratio to 2.4 times or more, it becomes possible to produce carbon fiber precursor acrylic fiber having sufficient molecular orientation, and as a result, it is possible to increase the strand strength of the carbon fiber bundle. Become. In addition, it is possible to prevent the center line average roughness Ra of the surface of the single fiber of the obtained carbon fiber precursor acrylic fiber from becoming too small. Further, by setting the draw ratio to 2.8 times or less, it is possible to prevent the destruction of the fibril structure and the formation of defective points of the carbon fiber precursor acrylic fiber due to excessive stretching, and as a result, the strand strength of the carbon fiber bundle is increased. It can be made higher. In addition, it is possible to prevent the center line average roughness Ra of the surface of the single fiber of the obtained carbon fiber precursor acrylic fiber from becoming too large. From the viewpoint of increasing the strand strength of the carbon fiber bundle and improving the performance of the CFRP tank, the draw ratio is more preferably 2.4 times or more and 2.7 times or less, and 2.5 times or more and 2.7 times or less. Is more preferable.

It is preferable to relax or stretch the yarn obtained by washing and drawing to 0.97 times or more and 1.1 times or less in hot water of 95 ° C. or higher and lower than 100 ° C. to obtain a drawn yarn. By setting the value to 0.97 times or more, it is possible to prevent poor take-up due to loosening of the fiber bundle, and it is possible to alleviate the distortion of stretching in the previous step. Further, by setting the value to 1.1 times or less, excessive stretching can be suppressed, and destruction of the fibril structure and formation of defective points of the carbon fiber precursor acrylic fiber can be prevented. From the viewpoint of increasing the strength of the carbon fiber and the production stability of the carbon fiber precursor acrylic fiber, the draw ratio in hot water is more preferably 0.97 times or more and 1.05 times or less.

The total draw ratio from the time when the coagulated yarn is taken up to the time when the coagulated yarn is drawn in hot water to obtain a drawn yarn is preferably 2.4 times or more and 2.9 times or less. By setting the value to 2.4 times or more, it becomes possible to produce carbon fiber precursor acrylic fibers having sufficient orientation, and as a result, it becomes possible to increase the strand strength of the carbon fiber bundle. In addition, it is possible to prevent the center line average roughness Ra of the surface of the single fiber of the obtained carbon fiber precursor acrylic fiber from becoming too small. Further, by setting the draw ratio to 2.9 times or less, it is possible to prevent the destruction of the fibril structure and the formation of defective points of the carbon fiber precursor acrylic fiber due to excessive stretching. In addition, it is possible to prevent the center line average roughness Ra of the surface of the single fiber of the obtained carbon fiber precursor acrylic fiber from becoming too large. From the viewpoint of increasing the strand strength of the carbon fiber bundle and improving the performance of the CFRP tank, the total draw ratio from the time when the coagulated yarn is taken up to the time when the coagulated yarn is drawn in water at 95 ° C. or higher and lower than 100 ° C. to obtain a drawn yarn. Is more preferably 2.4 times or more and 2.7 times or less, and further preferably 2.5 times or more and 2.7 times or less.

It is preferable to impart an oil composition to the drawn yarn obtained by drawing in water at 95 ° C. or higher and lower than 100 ° C. The oil composition can be determined in consideration of the functions required for the carbon fiber precursor acrylic fiber, for example, a silicone-based oil composition is preferable, and if necessary, an antioxidant, an antistatic agent, a defoaming agent, etc. Additives such as preservatives, antibacterial agents, and penetrants can be blended. As a method for applying the oil composition to the drawn yarn, a known method such as a roller method, a guide method, a spray method, or a dip method can be used. The drawn yarn to which the oil composition is attached is subsequently dried in a drying step to become dried fibers. This dried fiber can also be used as a carbon fiber precursor acrylic fiber.

In the drying step, the drawn yarn can be dried by a conventionally known method, and for example, drying with a heating roller is preferable as a drying method. The number of heating rollers may be one or two or more.

The dried fibers can also be stretched in a pressurized steam atmosphere to obtain carbon fiber precursor acrylic fibers. At this time, the temperature of the pressurized steam atmosphere is preferably 130 ° C. or higher and 160 ° C. or lower. Further, the stretching ratio in a pressurized steam atmosphere is preferably 3.0 times or more and 4.5 times or less.
By setting the temperature of the pressurized steam atmosphere to 130 ° C. or higher, the dry fibers are sufficiently plasticized, do not break even when the draw ratio is increased, and the amount of fluff contained in the obtained carbon fiber precursor acrylic fiber is reduced. As a result, the quality of the carbon fiber obtained by flame resistance and carbonization is stabilized. Further, by setting the temperature of the pressurized steam atmosphere to 160 ° C. or lower, the oxidation reaction and the decomposition reaction can be suppressed during stretching in the pressurized steam atmosphere, so that the resulting carbon fiber bundle strands can be suppressed. It is possible to prevent a decrease in strength.

By setting the draw ratio in a pressurized steam atmosphere to 3.0 times or more, the molecular orientation of the obtained carbon fiber precursor acrylic fiber is improved, and the strand strength of the obtained carbon fiber bundle is improved. Further, by setting the draw ratio in a pressurized steam atmosphere to 4.5 times or less, excessive stretching can be suppressed, and destruction of the fibril structure and formation of defective points of the carbon fiber precursor ackle fiber can be prevented. It will be possible.
From the viewpoint of increasing the strand strength of the carbon fiber bundle and improving the stretching stability, it is more preferable that the stretching ratio in a pressurized steam atmosphere is 3.3 times or more and 4.3 times or less.
The total draw ratio from the time when the coagulated yarn is taken up to the time when it is drawn in a pressurized steam atmosphere is preferably 9.0 times or more and 12 times or less. By setting the value to 9.0 times or more, it is possible to prevent insufficient molecular orientation of the carbon fiber precursor acrylic fiber due to insufficient stretching, and as a result, it is possible to increase the strand strength of the carbon fiber bundle. Further, by setting the total draw ratio to 12 times or less, it is possible to prevent the destruction of the fibril structure and the formation of defective points of the carbon fiber precursor acrylic fiber due to excessive stretching, and as a result, the strand strength of the carbon fiber bundle is increased. It becomes possible to do. From the viewpoint of increasing the strand strength of the carbon fiber bundle, it is more preferable that the total draw ratio is 9 times or more and 11 times or less.

The pressurized steam that creates the atmosphere in which the dried fibers are stretched is preferably pressurized saturated steam. The carbon fiber precursor acrylic fiber obtained after drying or stretching in a pressurized steam atmosphere is cooled to a room temperature state by a method such as contacting with a roll at room temperature. The cooled carbon fiber precursor acrylic fiber is wound on a bobbin by a winder or transferred to a Kens and stored, and is used for the production of carbon fiber.

From the above, the carbon fiber precursor acrylic fiber of the present invention can be preferably produced by a method including the following steps 1) to 3) and satisfying the following conditions 4) and 5).
1) Acrylonitrile-based polymer solution is discharged from a spinneret to coagulate in a coagulation liquid having a coagulation liquid concentration of 65% by mass or more and 70% by mass or less and a coagulation liquid temperature of 36 ° C. or more and 40 ° C. or less. A step of obtaining a yarn and at the same time taking it while controlling the tension applied to the coagulated yarn to 55 mgf / filament or more and 75 mgf / filament or less.
2) After the coagulated yarn taken in the above 1) step is drawn in the air at 1.00 times or more and 1.15 times or less, using water at 50 ° C. or higher, from 4 steps or more and 7 steps or less. Stretching / washing is performed in a magnification range of 2.4 times or more and 2.7 times or less in a washing / stretching tank, and 0.97 times or more and 1.1 times or less in a hot water tank using water at 95 ° C. or higher. A step of obtaining a drawn yarn by relaxing or drawing the above.
3) A step of applying an oil agent to the drawn yarn after drawing in the step 2), drying the yarn, and then stretching the yarn to 3.0 times or more and 4.5 times or less in a pressurized steam atmosphere of 130 ° C. or higher and 160 ° C. or lower.
4) The total draw ratio of the coagulated yarn from the time when the coagulated yarn in the step 1) is taken up to the time when the drawn yarn in the step 2) is obtained is 2.4 times or more and 2.7 times or less.
5) The total draw ratio from the time when the coagulated yarn in the step 1) is taken from the coagulating liquid to the time when the coagulated yarn in the step 3) is drawn in a pressurized steam atmosphere is 9.0 times or more and 12 times or less.

The carbon fiber of the present invention is obtained by making the above-mentioned carbon fiber precursor acrylic fiber flame-resistant and carbonized.
The carbon fiber of the present invention has a center line average roughness Ra of the surface of a single fiber of 6.0 nm or more and 13 nm or less.
In the present invention, by setting the centerline average roughness Ra of the surface of the single fiber of the carbon fiber to 6.0 nm or more, it is possible to suppress excessive focusing of the carbon fiber bundle made of the single fiber of the carbon fiber, and the carbon fiber bundle. Is easily impregnated with resin. Further, by setting the average roughness Ra of the center line of the surface of the carbon fiber single fiber to 13 nm or less, it is possible to prevent insufficient focusing of the carbon fiber bundle made of the carbon fiber single fiber, and to make the resin uniform in the carbon fiber bundle. Is easy to impregnate.
From the viewpoint of obtaining a high-strength CFRP tank, it is more preferable that the center line average roughness Ra of the single fiber surface of the carbon fiber is 10 nm or less. The center line average roughness Ra of the surface of the single fiber of the carbon fiber can be measured by the method described in the examples.

In the carbon fiber of the present invention, the major axis / minor axis of the single fiber of the carbon fiber is 1.11 or more and 1.245 or less. In the present invention, by setting the major axis / minor axis of the carbon fiber single fibers to 1.11 or more, it is possible to sufficiently secure a gap between the carbon fiber single fibers, and it becomes easy to impregnate the carbon fiber bundle with the resin. .. Further, by setting the major axis / minor axis of the carbon fiber single fibers to 1.245 or less, it is possible to prevent the gaps between the carbon fiber single fibers from becoming excessive, and it becomes easy to uniformly impregnate the carbon fiber bundle with the resin.
From the viewpoint of obtaining a high-strength CFRP tank, the major axis / minor axis of the carbon fiber single fiber is more preferably 1.135 or more. The major axis / minor axis of the single fiber of the carbon fiber is defined in the same manner as the major axis / minor axis of the single fiber of the carbon fiber precursor acrylic fiber, and can be measured by the same method.

The carbon fiber of the present invention preferably has a single fiber recess distance / minor axis of 0.011 or more and 0.018 or less.
In the present invention, by setting the recess distance / minor diameter of the carbon fiber single fibers to 0.011 or more, it is possible to sufficiently secure a gap between the carbon fiber single fibers, and the carbon fiber bundle is impregnated with the resin. It will be easier. Further, by setting the recess distance / minor axis of the carbon fiber single fibers to 0.018 or less, it is possible to prevent the gaps between the carbon fiber single fibers from becoming excessive, and it becomes easy to uniformly impregnate the carbon fiber bundle with the resin. ..
From the viewpoint of increasing the strength of the CFRP tank, it is more preferable that the recess distance / minor axis of the carbon fiber single fiber is 0.0145 or more. The dent distance / minor axis of the single fiber of the carbon fiber is defined in the same manner as the dent distance / minor axis of the single fiber of the carbon fiber precursor acrylic fiber, and can be measured by the same method.

The carbon fiber can be obtained by flame-resistant and carbonizing the carbon fiber precursor acrylic fiber. The conditions for flame resistance and carbonization are not particularly limited, but it is preferable to set conditions in which structural defects such as voids are unlikely to occur inside the fiber. In flame resistance, the carbon fiber precursor acrylic fiber is heated in an oxidizing atmosphere under tension or stretching conditions to obtain flame resistance. Examples of the flameproofing method include a hot air circulation method, a fixed hot plate method having a porous surface, a heating roll method, and the like. The heating temperature for flame resistance is preferably, for example, 200 ° C. or higher and 300 ° C. or lower. For flame resistance, it is preferable to treat until the density of the flame resistant fibers is 1.3 g / cm ³ or more and 1.5 g / cm ^{3 or less.}

In carbonization, carbon fibers are obtained by heating the flame-resistant fibers obtained by flame resistance in an inert gas atmosphere. Carbonization preferably consists of pre-carbonization and high-temperature carbonization. For precarbonization, the flame-resistant fibers are heated under tension in an inert gas atmosphere having a maximum temperature of 550 ° C. or higher and 800 ° C. or lower to obtain precarbonized fibers. This pre-carbonization can improve the mechanical properties of the carbon fibers. As the inert gas, known inert gases such as nitrogen, argon and helium can be used, but nitrogen is preferable from the viewpoint of economy.
In high-temperature carbonization, the pre-carbonized fibers are passed through an inert gas atmosphere of 1200 ° C. or higher and 3000 ° C. or lower, and the pre-carbonized fibers are heated to obtain carbon fibers. This high-temperature carbonization can improve the mechanical properties of carbon fibers. The inert gas that can be used is the same as that of the inert gas that can be used in the precarbonization operation.

From the above, the carbon fiber of the present invention can be preferably produced by a method including the following steps 7) to 9).
7) A flame-resistant step of heating a carbon fiber precursor acrylic fiber bundle composed of the carbon fiber precursor acrylic fiber of the present invention to 200 ° C. or higher and 300 ° C. or lower in an oxidizing atmosphere to form a flame-resistant fiber bundle.
8) A pre-carbonization step in which the flame-resistant fiber bundle is heated at 550 ° C. or higher and 800 ° C. or lower in a non-oxidizing atmosphere to form a pre-carbonized fiber bundle.
9) A high-temperature carbonization step in which the pre-carbonized fiber bundle is heated at 1200 ° C. or higher and 3000 ° C. or lower in a non-oxidizing atmosphere to form a carbon fiber bundle.

The obtained carbon fiber is preferably surface-treated. Examples of the surface treatment method include known methods, that is, oxidation treatment by electrolytic oxidation, chemical oxidation, air oxidation, or the like, and any of them may be used. After the electrolytic oxidation treatment, a cleaning treatment for removing the electrolyte on the surface of the carbon fibers and impurities adhering by the electrolytic oxidation treatment is performed, and the carbon fiber bundle is subsequently dried. As the drying method, any known technique such as roll drying, hot air drying and radiant heat drying can be adopted.

Next, it is preferable that the carbon fibers are sized. The sizing treatment can be carried out by applying a sizing solution obtained by dissolving a sizing agent in an organic solvent or an emulsion solution dispersed in water with an emulsifier or the like to the carbon fibers and drying the sizing solution. The amount of the sizing agent attached to the carbon fibers can be adjusted by adjusting the concentration of the sizing agent in the sizing solution or adjusting the amount of the sizing agent attached by the amount of drawing. As a method for adhering the sizing liquid to the carbon fibers, it is preferable to use a method in which running carbon fiber bundles are arranged in parallel at equal intervals to form a sheet and immersed in the sizing liquid from the viewpoint of productivity.
The carbon fiber thus obtained not only has high strand strength, but also has high strength in the CFRP tank manufactured by using the carbon fiber.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

[Coagulation thread take-up tension]
The tension at which the coagulated yarn discharged and formed from the nozzle withdraws the coagulated yarn bundle from the force applied to the first guide after being discharged from the coagulating liquid was measured, and the coagulated yarn withdrawal tension was calculated by converting it per filament.

[Major / minor diameter of single fiber]
A fiber bundle for measurement is passed through a tube made of vinyl chloride resin having an inner diameter of 1 mm, and then sliced into round slices with a knife to prepare a sample. Then, this sample was adhered to the SEM sample table with the fiber cross section facing upward, and gold was further sputtered to a thickness of about 10 nm, and then by an electron microscope (manufactured by Phillips, product name: XL20 scanning type). , The fiber cross section is observed under the conditions of an acceleration voltage of 7.00 kV and a working distance of 31 mm. Of the observed single fiber cross sections, 100 were randomly selected, the rectangle with the smallest area circumscribing each was obtained, the ratio of the length of the long side to the length of the short side was obtained, and the average value of the 100 fibers was obtained. Was defined as the major axis / minor axis of the single fiber of the fiber bundle.

[Center line average roughness Ra of single fiber surface]
Both ends of the fiber bundle for measurement are fixed with carbon paste on a metal sample table (20 mm diameter) for SPA400 (20 mm diameter) "Epolide Service Co., Ltd., product number: KY10200167" attached to the scanning probe microscope device, and under the following conditions. Measure.

[Scanning probe microscope measurement conditions]
Equipment: SPI4000 probe station, SPA400 (unit) manufactured by SII Nanotechnology Co., Ltd.
Scanning mode: Dynamic force mode (DFM) (shape image measurement)
Probe: SI-DF-20 manufactured by SII Nanotechnology Co., Ltd.
Scanning range: 2 μm x 2 μm
Rotation: 90 °
Scanning speed: 1.0Hz,
Number of pixels: 512 x 512
Measurement environment: room temperature, air
One image was obtained for one single fiber under the above conditions, and the obtained image was subjected to image analysis under the following conditions using image analysis software (SPIWin) attached to a scanning probe microscope.

[Image analysis conditions]
The obtained shape image is subjected to [flat processing], [median 8 processing], and [third-order tilt correction] to obtain an image in which a curved surface is fitted and corrected to a flat surface. The center line average roughness Ra is obtained from the surface roughness analysis of the plane-corrected image.

[Flat processing]
It is a process of removing distortions and waviness in the Z-axis direction appearing in image data due to lift, vibration, creep of a scanner, etc., and is a process of removing distortions of data due to a device factor in scanning probe microscope measurement.

[Median 8 processing]
All the Z-axis data of the obtained shape image is processed by the median filter in the range of 3 × 3.

[Third-order tilt correction]
A cubic curved surface is obtained and fitted by least squares approximation from all the data of the image to be processed.
In the measurement of the center line average roughness Ra of the single fiber surface of the fiber bundle, 10 single fibers were randomly collected for each fiber bundle, and images were obtained and analyzed with a scanning probe microscope for each of them, and the fiber surface was analyzed. The center line average roughness Ra is measured. The average value of 10 of the obtained Ra was defined as the center line average roughness Ra of the single fiber surface of the fiber bundle for measurement.

[Single fiber dent distance / minor diameter]
Similar to the measurement of the major axis / minor axis of the single fiber, the rectangle having the smallest area circumscribing each of the cross sections of 100 randomly selected single fibers was obtained, and the length of the short side thereof was measured. .. Further, the recess distance (see FIG. 2) was measured with respect to the same cross section. The ratio of the dent distance to the length of the short side measured in this way was calculated, and the average value of 100 of the calculated ratios was taken as the dent distance / minor diameter of the single fiber of the fiber bundle. For each single fiber, one of the long sides of the rectangle 2 having the smallest area circumscribing the cross section 1 often coincides with the straight line 3 obtained to determine the recessed distance of the cross section 1 (FIGS. 3 and 5). ), But may not match (Fig. 2). Further, when the straight line tangent to the cross section 1 at two points cannot be obtained because the circumference of the cross section 1 is a convex curve (FIG. 4), the recess distance Z is treated as 0.

[Strand strength of carbon fiber bundle]
The strand strength of the carbon fiber bundle was measured according to the epoxy resin impregnated strand method specified in JIS-R-7608. The number of measurements was 10 times, and the average value was used as the evaluation target.

[Destructive pressure of pressure vessel]
Using a filament winding device, the carbon fiber bundle was wound around an aluminum liner having a capacity of 9 liters (total length 540 mm, body length 415 mm, body outer diameter 163 mm, wall thickness 3 mm at the center of the body). The aluminum liner used is made of a heat-treated aluminum material specified in JIS H 4040 A6061-T6. The position of the carbon fiber bundle is adjusted via the unwinding guide roll, and then the matrix resin is quantitatively supplied and impregnated into the carbon fiber bundle using the touch roll, and then wound around the liner to prepare an intermediate container. did. Regarding how to wrap the liner, first, a hoop layer forming 88.6 ° with respect to the rotation axis direction of the liner is formed on the body, and the liner is wound at an angle of 11.0 ° with respect to the rotation axis direction of the liner. After laminating the helical layer that reinforces the mirror part, a hoop layer forming 65.0 ° with respect to the rotation axis direction of the liner is formed on the body, and then an angle of 13.0 ° with respect to the rotation axis direction of the liner is formed. A helical layer that reinforces the mirror part of the liner is laminated, and a hoop layer that forms 88.6 ° with respect to the rotation axis direction of the liner is formed again on the body portion, and 11.0 ° with respect to the rotation axis direction of the liner. A helical layer was laminated to reinforce the mirror part of the liner at an angle.
The obtained intermediate container was removed from the filament winding apparatus, suspended in a heating furnace, the temperature in the furnace was raised to 110 ° C. at 2 ° C./min, and then held at 110 ° C. for 2 hours for curing. Then, the temperature in the furnace was cooled to 60 ° C. at 1 ° C./min to obtain a CFRP tank.
After setting the CFRP tank in the hydraulic failure tester and filling the CFRP tank with water, the CFRP tank is loaded with water pressure at a boosting speed of 15 MPa / min, and the water pressure when the CFRP tank bursts is recorded. The breaking pressure of the CFRP tank was used.

Example 1
[Manufacturing of acrylonitrile-based polymer solution]
Acrylonitrile, acrylamide, and methacrylic acid are put into water and copolymerized by aqueous suspension polymerization in the presence of ammonium persulfate-ammonium hydrogen sulfite and iron sulfate, and acrylonitrile unit / acrylamide unit / methacrylic acid unit = 97/2/1. An acrylonitrile-based polymer composed of (mass ratio) was obtained. This acrylonitrile-based polymer was dissolved in dimethylacetamide to prepare a 21% by mass acrylonitrile-based polymer solution.

[Manufacturing of carbon fiber precursor acrylic fiber bundle]
The acrylonitrile-based polymer solution obtained above is discharged into a coagulating solution consisting of a dimethylacetamide aqueous solution having a concentration of 67% by mass and a temperature of 38 ° C. from a spinning nozzle having a pore size of 50 μm and a pore number of 30,000 to obtain a coagulated yarn and at the same time coagulate. The tension applied to the yarn was taken while controlling it to 70 mgf / filament.
The collected coagulated yarn is stretched 1.01 times in the air, and then 2.60 times stretched and washed at the same time through a 5-stage stretching / washing tank using water in the range of 50 ° C. to 98 ° C. After that, drawing (relaxation) of 0.98 times was carried out in a hot water tank using water at 98 ° C. to obtain drawn yarn. The obtained drawn yarn was immersed in an amino-modified silicone-based oil dispersion and densified with a heating roller at 140 ° C. to obtain a dried fiber bundle. The amino-modified silicone-based oil dispersion used at this time was an emulsifier (manufactured by Nikko Chemicals Co., Ltd., trade name: NIKKOL BL) with respect to 85 parts by mass of amino-modified silicone (manufactured by Shinetsu Chemical Industry Co., Ltd., trade name: KF-865). A mixture of 15 parts by mass of -9EX) was emulsified with a Gorin mixer (manufactured by SMT Co., Ltd., trade name: pressure homogenizer Gorin type), and then water was added to produce the product. The total draw ratio from the time when the coagulated yarn was taken up to the time when the drawn yarn after the treatment in the hot water tank was obtained was 2.57 times. Next, the obtained dried fiber bundle was stretched 3.50 times in a pressurized saturated steam atmosphere at about 150 ° C. to produce a carbon fiber precursor acrylic fiber bundle having a single fiber fineness of 1.0 dtex. The total draw ratio from the time when the coagulated yarn was taken up to the time when the coagulated yarn was drawn under a pressurized saturated steam atmosphere was 9.01 times.
Table 1 summarizes the spinning conditions for the carbon fiber precursor acrylic fiber bundle. Further, the physical characteristics of the obtained carbon fiber precursor acrylic fiber bundle (major axis / minor axis of the single fiber, recessed distance / minor axis of the single fiber, and centerline average roughness Ra of the surface of the single fiber) were measured according to the above method. The measurement results are shown in Table 2.

[Manufacturing of carbon fiber bundles]
The obtained carbon fiber precursor acrylic fiber bundle is introduced into a flameproof furnace, and air heated to 220 to 280 ° C. is blown onto the carbon fiber precursor acrylic fiber bundle to make the precursor fiber bundle flameproof and have a density of 1. A flame resistant fiber bundle of .35 g / cm ^{3 was obtained.} The elongation rate was -4.0%, and the flame resistance treatment time was 70 minutes.
The flame-resistant fiber bundle was then passed through a first carbonization furnace with a temperature gradient of 300-700 ° C. in nitrogen with an elongation of 4.0%. The temperature gradient in the first carbonization furnace was set to be linear, and the treatment time was 1.3 minutes. Further, a carbon fiber bundle was obtained by passing through a second carbonization furnace having a temperature gradient of 1000 to 1600 ° C. in a nitrogen atmosphere while applying an elongation of −4.5%. The processing time in the second carbonization furnace was 1.3 minutes.
Subsequently, the carbon fiber bundle was used as an anode by running in a 10% by mass aqueous solution of ammonium bicarbonate, and energization treatment was performed between the counter electrode and the counter electrode so that the amount of electricity was 30 coulombs per 1 g of carbon fiber to be treated, and water at 50 ° C. After washing with, it was dried.
Next, an aqueous dispersion of Hydran N320 (manufactured by DIC Corporation) was applied, dried, and 0.8% by mass of a sizing agent was adhered to the bobbin.
Physical properties of the obtained carbon fiber bundle (major axis / minor axis of single fiber, recess distance / minor axis of single fiber, centerline average roughness Ra of single fiber surface, strand strength and produced using the obtained carbon fiber bundle. The breaking pressure of the pressure vessel) was measured according to the above method. The measurement results are shown in Table 2.

Example 2
In the production of the carbon fiber precursor acrylic fiber bundle, the acrylonitrile-based polymer solution used in Example 1 was taken up using a nozzle having a pore size of 45 μm while controlling the tension applied to the coagulated yarn to 60 mgf / filament, and was saturated under pressure. The same procedure as in Example 1 was carried out except that the stretching ratio in a water vapor atmosphere was set to 4.20 times. The total draw ratio from taking the coagulated yarn to obtaining the drawn yarn after treatment in the hot water tank is 2.57 times, and the total draw ratio from taking the coagulated yarn to drawing in a pressurized saturated steam atmosphere is 10. It was 0.8 times.
Table 1 summarizes the spinning conditions for the carbon fiber precursor acrylic fiber bundle. The physical properties of the obtained carbon fiber precursor acrylic fiber bundle (major axis / minor axis of the single fiber, recessed distance / minor axis of the single fiber, and centerline average roughness Ra of the surface of the single fiber), and the obtained carbon fiber bundle. Physical properties (major axis / minor axis of single fiber, recess distance / minor axis of single fiber, centerline average roughness Ra of single fiber surface, strand strength and breaking pressure of pressure vessel manufactured using the obtained carbon fiber bundle ) Was measured according to the above method. The measurement results are shown in Table 2.

Example 3
In the production of the carbon fiber precursor acrylic fiber bundle, the acrylonitrile-based polymer solution used in Example 1 was taken up while controlling the tension applied to the coagulated yarn to 72 mgf / filament, and the draw ratio under a pressurized saturated steam atmosphere was adjusted. It was carried out in the same manner as in Example 1 except that it was set to 4.20 times. The total draw ratio from taking the coagulated yarn to obtaining the drawn yarn after treatment in the hot water tank is 2.57 times, and the total draw ratio from taking the coagulated yarn to drawing in a pressurized saturated steam atmosphere is 10. It was 0.8 times.
Table 1 summarizes the spinning conditions for the carbon fiber precursor acrylic fiber bundle. The physical properties of the obtained carbon fiber precursor acrylic fiber bundle (major axis / minor axis of the single fiber, recessed distance / minor axis of the single fiber, and centerline average roughness Ra of the surface of the single fiber), and the obtained carbon fiber bundle. Physical properties (major axis / minor axis of single fiber, recess distance / minor axis of single fiber, centerline average roughness Ra of single fiber surface, strand strength and breaking pressure of pressure vessel manufactured using the obtained carbon fiber bundle ) Was measured according to the above method. The measurement results are shown in Table 2.

Example 4
In the production of the carbon fiber precursor acrylic fiber bundle, the same procedure as in Example 1 was carried out except that the concentration of the dimethylacetamide aqueous solution as the coagulating liquid was set to 69% by mass and the tension applied to the coagulated yarn was controlled to 65 mgf / filament.
Table 1 summarizes the spinning conditions for the carbon fiber precursor acrylic fiber bundle. The physical properties of the obtained carbon fiber precursor acrylic fiber bundle (major axis / minor axis of the single fiber, recessed distance / minor axis of the single fiber, and centerline average roughness Ra of the surface of the single fiber), and the obtained carbon fiber bundle. Physical properties (major axis / minor axis of single fiber, recess distance / minor axis of single fiber, centerline average roughness Ra of single fiber surface, strand strength and breaking pressure of pressure vessel manufactured using the obtained carbon fiber bundle ) Was measured according to the above method. The measurement results are shown in Table 2.

Reference example 1
In the production of the carbon fiber precursor acrylic fiber, the same procedure as in Example 1 was carried out except that the temperature of the dimethylacetamide aqueous solution as the coagulating liquid was set to 35 ° C. and the tension applied to the coagulated yarn was controlled to 74 mgf / filament.
Table 1 summarizes the spinning conditions for the carbon fiber precursor acrylic fiber bundle. The physical properties of the obtained carbon fiber precursor acrylic fiber bundle (major axis / minor axis of the single fiber, recessed distance / minor axis of the single fiber, and centerline average roughness Ra of the surface of the single fiber), and the obtained carbon fiber bundle. Physical properties (major axis / minor axis of single fiber, recess distance / minor axis of single fiber, centerline average roughness Ra of single fiber surface, strand strength and breaking pressure of pressure vessel manufactured using the obtained carbon fiber bundle ) Was measured according to the above method. The measurement results are shown in Table 2.

Reference example 2
In the production of the carbon fiber precursor acrylic fiber bundle, the same procedure as in Example 1 was carried out except that the draw ratio in the drawing / washing tank was set to 2.80 times. The total draw ratio from taking the coagulated yarn to obtaining the drawn yarn after treatment in the hot water tank is 2.77 times, and the total draw ratio from taking the coagulated yarn to drawing in a pressurized saturated steam atmosphere is 9. It was .70 times.
Table 1 summarizes the spinning conditions for the carbon fiber precursor acrylic fiber bundle. The physical properties of the obtained carbon fiber precursor acrylic fiber bundle (major axis / minor axis of the single fiber, recessed distance / minor axis of the single fiber, and centerline average roughness Ra of the surface of the single fiber), and the obtained carbon fiber bundle. Physical properties (major axis / minor axis of single fiber, recess distance / minor axis of single fiber, centerline average roughness Ra of single fiber surface, strand strength and breaking pressure of pressure vessel manufactured using the obtained carbon fiber bundle ) Was measured according to the above method. The measurement results are shown in Table 2.

Comparative Example 1
In the production of the carbon fiber precursor acrylic fiber bundle, the acrylonitrile-based polymer solution used in Example 1 was placed in a coagulating solution consisting of a dimethylacetamide aqueous solution having a concentration of 65% by mass and a temperature of 30 ° C. and having a pore size of 75 μm and a pore size of 30,000. At the same time as the coagulated yarn was discharged from the spinning nozzle, the tension applied to the coagulated yarn was taken over while being controlled to 60 mgf / filament. The collected coagulated yarn was not stretched in the air, but was again stretched at a concentration of 65% by mass and at a temperature of 30 ° C. in a dimethylacetamide aqueous solution at a ratio of 2.00 times. After that, the same procedure as in Example 1 was carried out except that the stretching ratio in the stretching / washing tank was 4.00 times and the stretching ratio in a pressurized saturated steam atmosphere was 2.00 times. The total draw ratio from taking the coagulated yarn to obtaining the drawn yarn after treatment in the hot water tank is 7.84 times, and the total draw ratio from taking the coagulated yarn to drawing in a pressurized saturated steam atmosphere is 15. It was 7.7 times.
Table 1 summarizes the spinning conditions for the carbon fiber precursor acrylic fiber bundle. The physical properties of the obtained carbon fiber precursor acrylic fiber bundle (major axis / minor axis of the single fiber, recessed distance / minor axis of the single fiber, and centerline average roughness Ra of the surface of the single fiber), and the obtained carbon fiber bundle. Physical properties (major axis / minor axis of single fiber, recess distance / minor axis of single fiber, centerline average roughness Ra of single fiber surface, strand strength and breaking pressure of pressure vessel manufactured using the obtained carbon fiber bundle ) Was measured according to the above method. The measurement results are shown in Table 2.
The major axis / minor axis of the carbon fiber precursor acrylic fiber bundle and the single fiber of the carbon fiber bundle were almost the same, but the dent distance / minor axis of the single fiber and the center line average roughness Ra of the single fiber surface were found in Example 1. Increased compared to. Further, the strand strength of the carbon fiber bundle was 4400 MPa, and the breaking pressure of the pressure vessel was 80 MPa, which was lower than that of Example 1.

Comparative Example 2
In the production of the carbon fiber precursor acrylic fiber bundle, the acrylonitrile-based polymer solution used in Example 1 was placed in a coagulating solution consisting of a dimethylacetamide aqueous solution having a concentration of 60% by mass and a temperature of 30 ° C., having a pore size of 75 μm and a pore size of 30,000. At the same time as the coagulated yarn was discharged from the spinning nozzle, the tension applied to the coagulated yarn was taken over while being controlled to 95 mgf / filament. The coagulated yarn taken up was not stretched in the air, but was stretched again in a dimethylacetamide aqueous solution having a concentration of 60% by mass and a temperature of 30 ° C. at a concentration of 1.20 times. After that, the same procedure as in Example 1 was carried out except that the stretching ratio in the stretching / washing tank was 4.00 times and the stretching ratio in a pressurized saturated steam atmosphere was 2.00 times. The total draw ratio from taking the coagulated yarn to obtaining the drawn yarn after treatment in the hot water tank is 4.70 times, and the total draw ratio from taking the coagulated yarn to drawing in a pressurized saturated steam atmosphere is 9. It was .41 times.
Table 1 summarizes the spinning conditions for the carbon fiber precursor acrylic fiber bundle. The physical properties of the obtained carbon fiber precursor acrylic fiber bundle (major axis / minor axis of the single fiber, recessed distance / minor axis of the single fiber, and centerline average roughness Ra of the surface of the single fiber), and the obtained carbon fiber bundle. Physical properties (major axis / minor axis of single fiber, recess distance / minor axis of single fiber, centerline average roughness Ra of single fiber surface, strand strength and breaking pressure of pressure vessel manufactured using the obtained carbon fiber bundle ) Was measured according to the above method. The measurement results are shown in Table 2.
The major axis / minor axis of the carbon fiber precursor acrylic fiber bundle and the single fiber of the carbon fiber bundle, the recessed distance / minor axis of the single fiber, and the centerline average roughness Ra of the single fiber surface were increased as compared with Example 1. Further, the strand strength of the carbon fiber bundle was 4400 MPa, and the breaking pressure of the pressure vessel was 80 MPa, which was lower than that of Example 1.

Comparative Example 3
In the production of the carbon fiber precursor acrylic fiber bundle, the acrylonitrile-based polymer solution used in Example 1 was taken up while controlling the tension applied to the coagulated yarn to 74 mgf / filament, and the draw ratio in the air was set to 1.05 times. The same procedure as in Example 1 was carried out except that the stretching ratio in the stretching / washing tank was set to 3.00 times. The total draw ratio from taking the coagulated yarn to obtaining the drawn yarn after treatment in the hot water tank is 3.09 times, and the total draw ratio from taking the coagulated yarn to drawing in a pressurized saturated steam atmosphere is 10. It was 0.8 times.
Table 1 summarizes the spinning conditions for the carbon fiber precursor acrylic fiber bundle. The physical properties of the obtained carbon fiber precursor acrylic fiber bundle (major axis / minor axis of the single fiber, recessed distance / minor axis of the single fiber, and centerline average roughness Ra of the surface of the single fiber), and the obtained carbon fiber bundle. Physical properties (major axis / minor axis of single fiber, recess distance / minor axis of single fiber, centerline average roughness Ra of single fiber surface, strand strength and breaking pressure of pressure vessel manufactured using the obtained carbon fiber bundle ) Was measured according to the above method. The measurement results are shown in Table 2.
The major axis / minor axis of the carbon fiber precursor acrylic fiber bundle and the single fiber of the carbon fiber bundle, the recessed distance / minor axis of the single fiber, and the centerline average roughness Ra of the single fiber surface were reduced as compared with Example 1. Further, the strand strength of the carbon fiber bundle was also 5500 MPa, and the breaking pressure of the pressure vessel was 110 MPa, which was lower than that of Example 1.

Comparative Example 4
In the production of carbon fiber precursor acrylic fiber bundles, the draw ratio in the air was set to 1.20 times, the draw ratio in the draw / washing tank was set to 4.00 times, and the draw ratio in a pressurized saturated steam atmosphere was set to 2. It was carried out in the same manner as in Example 1 except that it was set to .60 times. The total draw ratio from the time when the coagulated yarn is taken up to the time when the drawn yarn after treatment in the hot water tank is obtained is 4.70 times, and the total draw ratio from the time when the coagulated yarn is taken up to the time when it is drawn under a pressurized saturated steam atmosphere is 12. It was twice as much.
Table 1 summarizes the spinning conditions for the carbon fiber precursor acrylic fiber bundle. The physical properties of the obtained carbon fiber precursor acrylic fiber bundle (major axis / minor axis of the single fiber, recessed distance / minor axis of the single fiber, and centerline average roughness Ra of the surface of the single fiber), and the obtained carbon fiber bundle. Physical properties (major axis / minor axis of single fiber, recess distance / minor axis of single fiber, centerline average roughness Ra of single fiber surface, strand strength and breaking pressure of pressure vessel manufactured using the obtained carbon fiber bundle ) Was measured according to the above method. The measurement results are shown in Table 2.
The average roughness Ra of the centerline surface of the carbon fiber precursor acrylic fiber bundle and the single fiber surface of the carbon fiber bundle was almost the same as that of Example 1, but the major axis / minor axis of the single fiber and the recessed distance / minor axis of the single fiber. Was lower than that of Example 1. Further, the strand strength of the carbon fiber bundle was 5350 MPa, and the breaking pressure of the pressure vessel was 110 MPa, which was lower than that of Example 1.

Comparative Example 5
In the production of the carbon fiber precursor acrylic fiber bundle, the acrylonitrile-based polymer solution used in Example 1 was taken up while controlling the tension applied to the coagulated yarn to 49 mgf / filament, and then the taken coagulated yarn was taken in the air. After stretching 0.05 times, it was stretched 1.50 times in a dimethylacetamide aqueous solution having a concentration of 35% by mass and a temperature of 55 ° C. After that, the same procedure as in Example 1 was carried out except that the stretching ratio in the stretching / washing tank was 1.70 times and the stretching ratio in the hot water tank was 2.00 times. The total draw ratio from taking the coagulated yarn to obtaining the drawn yarn after treatment in the hot water tank is 5.36 times, and the total draw ratio from taking the coagulated yarn to drawing in a pressurized saturated steam atmosphere is 18. It was 7.7 times.
Table 1 summarizes the spinning conditions for the carbon fiber precursor acrylic fiber bundle. The physical properties of the obtained carbon fiber precursor acrylic fiber bundle (major axis / minor axis of the single fiber, recessed distance / minor axis of the single fiber, and centerline average roughness Ra of the surface of the single fiber), and the obtained carbon fiber bundle. Physical properties (major axis / minor axis of single fiber, recess distance / minor axis of single fiber, centerline average roughness Ra of single fiber surface, strand strength and breaking pressure of pressure vessel manufactured using the obtained carbon fiber bundle ) Was measured according to the above method. The measurement results are shown in Table 2.
The major axis / minor axis of the carbon fiber precursor acrylic fiber bundle and the single fiber of the carbon fiber bundle, and the center line average roughness Ra of the surface of the single fiber were lowered as compared with Example 1. No dents in the single fibers were observed (single fiber dent distance / minor axis = 0.000). Although the strand strength of the carbon fiber bundle was 6000 MPa, which was higher than that of Example 1, the breaking pressure of the pressure vessel was 120 MPa, which was lower than that of Example 1.

Comparative Example 6
In the production of the carbon fiber precursor acrylic fiber bundle, the temperature of the dimethylacetamide aqueous solution, which is a coagulating liquid, is set to 30 ° C., the tension applied to the coagulated yarn is controlled to 85 mgf / filament, and the draw ratio under a pressurized saturated steam atmosphere is 4. It was carried out in the same manner as in Example 1 except that it was multiplied by 20. The total draw ratio from taking the coagulated yarn to obtaining the drawn yarn after treatment in the hot water tank is 2.57 times, and the total draw ratio from taking the coagulated yarn to drawing in a pressurized saturated steam atmosphere is 10. It was 0.8 times.
Table 1 summarizes the spinning conditions for the carbon fiber precursor acrylic fiber bundle. The physical properties of the obtained carbon fiber precursor acrylic fiber bundle (major axis / minor axis of the single fiber, recessed distance / minor axis of the single fiber, and centerline average roughness Ra of the surface of the single fiber), and the obtained carbon fiber bundle. Physical properties (major axis / minor axis of single fiber, recess distance / minor axis of single fiber, centerline average roughness Ra of single fiber surface, strand strength and breaking pressure of pressure vessel manufactured using the obtained carbon fiber bundle ) Was measured according to the above method. The measurement results are shown in Table 2.
The major axis / minor axis of the carbon fiber precursor acrylic fiber bundle and the single fiber of the carbon fiber bundle, the recessed distance / minor axis of the single fiber, and the centerline average roughness Ra of the single fiber surface were increased as compared with Example 1. Although the strand strength of the carbon fiber bundle was 6000 MPa, which was higher than that of Example 1, the breaking pressure of the pressure vessel was 123 MPa, which was lower than that of Example 1.

Comparative Example 7
In the production of the carbon fiber precursor acrylic fiber bundle, the concentration of the dimethylacetamide aqueous solution, which is a coagulating liquid, is set to 63% by mass, the tension applied to the coagulated yarn is controlled to 88 mgf / filament, and the draw ratio under a pressurized saturated steam atmosphere is adjusted. It was carried out in the same manner as in Example 1 except that it was set to 4.20 times. The total draw ratio from taking the coagulated yarn to obtaining the drawn yarn after treatment in the hot water tank is 2.57 times, and the total draw ratio from taking the coagulated yarn to drawing in a pressurized saturated steam atmosphere is 10. It was 0.8 times.
Table 1 summarizes the spinning conditions for the carbon fiber precursor acrylic fiber bundle. The physical properties of the obtained carbon fiber precursor acrylic fiber bundle (major axis / minor axis of the single fiber, recessed distance / minor axis of the single fiber, and centerline average roughness Ra of the surface of the single fiber), and the obtained carbon fiber bundle. Physical properties (major axis / minor axis of single fiber, recess distance / minor axis of single fiber, centerline average roughness Ra of single fiber surface, strand strength and breaking pressure of pressure vessel manufactured using the obtained carbon fiber bundle ) Was measured according to the above method. The measurement results are shown in Table 2.
The major axis / minor axis of the carbon fiber precursor acrylic fiber bundle and the single fiber of the carbon fiber bundle, the recessed distance / minor axis of the single fiber, and the centerline average roughness Ra of the single fiber surface were increased as compared with Example 1. Although the strand strength of the carbon fiber bundle was 6000 MPa, which was higher than that of Example 1, the breaking pressure of the pressure vessel was 122 MPa, which was lower than that of Example 1.

Comparative Example 8
In the production of the carbon fiber precursor acrylic fiber bundle, the concentration of the dimethylacetamide aqueous solution, which is a coagulating liquid, is set to 65% by mass, the tension applied to the coagulated yarn is controlled to 68 mgf / filament, and stretching is performed without stretching in the air. The same procedure as in Example 1 was carried out except that the stretching ratio in the washing tank was 3.40 times and the stretching ratio in a pressurized saturated steam atmosphere was 2.00 times. The total draw ratio from taking the coagulated yarn to obtaining the drawn yarn after treatment in the hot water tank is 3.33 times, and the total draw ratio from taking the coagulated yarn to drawing in a pressurized saturated steam atmosphere is 6. It was .66 times.
Table 1 summarizes the spinning conditions for the carbon fiber precursor acrylic fiber bundle. The physical properties of the obtained carbon fiber precursor acrylic fiber bundle (major axis / minor axis of the single fiber, recessed distance / minor axis of the single fiber, and centerline average roughness Ra of the surface of the single fiber), and the obtained carbon fiber bundle. Physical properties (major axis / minor axis of single fiber, recess distance / minor axis of single fiber, centerline average roughness Ra of single fiber surface, strand strength and breaking pressure of pressure vessel manufactured using the obtained carbon fiber bundle ) Was measured according to the above method. The measurement results are shown in Table 2.
The major axis / minor axis of the carbon fiber precursor acrylic fiber bundle and the single fiber of the carbon fiber bundle and the recessed distance / minor axis of the single fiber were lower than those in Example 1, and the centerline average roughness Ra of the single fiber surface was It increased as compared with Example 1. The strand strength of the carbon fiber bundle was 4600 MPa, and the breaking pressure of the pressure vessel was 90 MPa, which were lower than those of Example 1.

Comparative Example 9
In the production of the carbon fiber precursor acrylic fiber bundle, the acrylonitrile-based polymer solution used in Example 1 was taken up while controlling the tension applied to the coagulated yarn to 45 mgf / filament, and the draw ratio in the air was set to 1.30 times. Examples except that the stretching ratio in the stretching / washing tank was 2.00 times, the stretching ratio in the hot water tank was 1.00 times, and the stretching ratio in a pressurized saturated steam atmosphere was 5.00 times. It was carried out in the same manner as in 1. The total draw ratio from taking the coagulated yarn to obtaining the drawn yarn after treatment in the hot water tank is 2.60 times, and the total draw ratio from taking the coagulated yarn to drawing in a pressurized saturated steam atmosphere is 13. It was 0.0 times.
Table 1 summarizes the spinning conditions for the carbon fiber precursor acrylic fiber bundle. The physical properties of the obtained carbon fiber precursor acrylic fiber bundle (major axis / minor axis of the single fiber, recessed distance / minor axis of the single fiber, and centerline average roughness Ra of the surface of the single fiber), and the obtained carbon fiber bundle. Physical properties (major axis / minor axis of single fiber, recess distance / minor axis of single fiber, centerline average roughness Ra of single fiber surface, strand strength and breaking pressure of pressure vessel manufactured using the obtained carbon fiber bundle ) Was measured according to the above method. The measurement results are shown in Table 2.
The major axis / minor axis of the carbon fiber precursor acrylic fiber bundle and the single fiber of the carbon fiber bundle and the center line average roughness Ra of the surface of the single fiber were lowered as compared with Example 1. No dents in the single fibers were observed (single fiber dent distance / minor axis = 0.000). The strand strength of the carbon fiber bundle was 5400 MPa, and the breaking pressure of the pressure vessel was 110 MPa, which were lower than those of Example 1.

Comparative Example 10
The production of the carbon fiber precursor acrylic fiber bundle was carried out in the same manner as in Example 1 except that the concentration of the dimethylacetamide aqueous solution in the coagulating liquid was 75%.
As a result, the single fibers of the coagulated yarn taken from the coagulating liquid adhered to each other, and the carbon fiber precursor acrylic fiber bundle could not be obtained. The spinning conditions for the carbon fiber precursor acrylic fiber bundle are as shown in Table 1.

Example 5
In the production of the carbon fiber precursor acrylic fiber bundle, the concentration of the dimethylacetamide aqueous solution, which is a coagulating liquid, is set to 68% by mass, the tension applied to the coagulated yarn is controlled to 74 mgf / filament, and the draw ratio in the air is 1.04 times. It was carried out in the same manner as in Example 1 except that it was carried out. The total draw ratio from taking the coagulated yarn to obtaining the drawn yarn after treatment in the hot water tank is 2.65 times, and the total draw ratio from taking the coagulated yarn to drawing in a pressurized saturated steam atmosphere is 9. It was .27 times.
Table 1 summarizes the spinning conditions for the carbon fiber precursor acrylic fiber bundle. The physical properties of the obtained carbon fiber precursor acrylic fiber bundle (major axis / minor axis of the single fiber, recessed distance / minor axis of the single fiber, and centerline average roughness Ra of the surface of the single fiber), and the obtained carbon fiber bundle. Physical properties (major axis / minor axis of single fiber, recess distance / minor axis of single fiber, centerline average roughness Ra of single fiber surface, strand strength and breaking pressure of pressure vessel manufactured using the obtained carbon fiber bundle ) Was measured according to the above method. The measurement results are shown in Table 2.

Example 6
In the production of the carbon fiber precursor acrylic fiber bundle, the acrylonitrile-based polymer solution used in Example 1 was taken up while controlling the tension applied to the coagulated yarn to 74 mgf / filament, and the stretching ratio in the stretching / washing tank was 2. The same procedure as in Example 1 was carried out except that the stretching ratio was set to 50 times and the stretching ratio in a pressurized saturated steam atmosphere was set to 3.80 times. The total draw ratio from taking the coagulated yarn to obtaining the drawn yarn after treatment in the hot water tank is 2.47 times, and the total draw ratio from taking the coagulated yarn to drawing in a pressurized saturated steam atmosphere is 9. It was .40 times.
Table 1 summarizes the spinning conditions for the carbon fiber precursor acrylic fiber bundle. The physical properties of the obtained carbon fiber precursor acrylic fiber bundle (major axis / minor axis of the single fiber, recessed distance / minor axis of the single fiber, and centerline average roughness Ra of the surface of the single fiber), and the obtained carbon fiber bundle. Physical properties (major axis / minor axis of single fiber, recess distance / minor axis of single fiber, centerline average roughness Ra of single fiber surface, strand strength and breaking pressure of pressure vessel manufactured using the obtained carbon fiber bundle ) Was measured according to the above method. The measurement results are shown in Table 2.

Example 7
In the production of the carbon fiber precursor acrylic fiber bundle, the concentration and temperature of the dimethylacetamide aqueous solution, which is a coagulating liquid, are set to 68% by mass and 39 ° C., respectively, the tension applied to the coagulated yarn is controlled to 60 mgf / filament, and the draw ratio in the air. Was 1.04 times, and the stretching ratio under a pressurized saturated steam atmosphere was 3.40 times, but the same procedure as in Example 1 was carried out. The total draw ratio from taking the coagulated yarn to obtaining the drawn yarn after treatment in the hot water tank is 2.65 times, and the total draw ratio from taking the coagulated yarn to drawing in a pressurized saturated steam atmosphere is 9. It was 0.01 times.
Table 1 summarizes the spinning conditions for the carbon fiber precursor acrylic fiber bundle. The physical properties of the obtained carbon fiber precursor acrylic fiber bundle (major axis / minor axis of the single fiber, recessed distance / minor axis of the single fiber, and centerline average roughness Ra of the surface of the single fiber), and the obtained carbon fiber bundle. Physical properties (major axis / minor axis of single fiber, recess distance / minor axis of single fiber, centerline average roughness Ra of single fiber surface, strand strength and breaking pressure of pressure vessel manufactured using the obtained carbon fiber bundle ) Was measured according to the above method. The measurement results are shown in Table 2.

Example 8
In the production of the carbon fiber precursor acrylic fiber bundle, the concentration and temperature of the dimethylacetamide aqueous solution as a coagulating liquid were set to 68% by mass and 39 ° C., respectively, the stretching ratio in the air was set to 1.04 times, and the atmosphere was pressurized saturated steam. The same procedure as in Example 1 was carried out except that the stretching ratio was set to 3.40 times. The total draw ratio from taking the coagulated yarn to obtaining the drawn yarn after treatment in the hot water tank is 2.65 times, and the total draw ratio from taking the coagulated yarn to drawing in a pressurized saturated steam atmosphere is 9. It was 0.01 times.
Table 1 summarizes the spinning conditions for the carbon fiber precursor acrylic fiber bundle. The physical properties of the obtained carbon fiber precursor acrylic fiber bundle (major axis / minor axis of the single fiber, recessed distance / minor axis of the single fiber, and centerline average roughness Ra of the surface of the single fiber), and the obtained carbon fiber bundle. Physical properties (major axis / minor axis of single fiber, recess distance / minor axis of single fiber, centerline average roughness Ra of single fiber surface, strand strength and breaking pressure of pressure vessel manufactured using the obtained carbon fiber bundle ) Was measured according to the above method. The measurement results are shown in Table 2.

Example 9
The production of the carbon fiber precursor acrylic fiber bundle was carried out in the same manner as in Example 1 except that the draw ratio in a pressurized saturated water vapor atmosphere was set to 4.20 times. The total draw ratio from taking the coagulated yarn to obtaining the drawn yarn after treatment in the hot water tank is 2.57 times, and the total draw ratio from taking the coagulated yarn to drawing in a pressurized saturated steam atmosphere is 10. It was 0.8 times.
Table 1 summarizes the spinning conditions for the carbon fiber precursor acrylic fiber bundle. The physical properties of the obtained carbon fiber precursor acrylic fiber bundle (major axis / minor axis of the single fiber, recessed distance / minor axis of the single fiber, and centerline average roughness Ra of the surface of the single fiber), and the obtained carbon fiber bundle. Physical properties (major axis / minor axis of single fiber, recess distance / minor axis of single fiber, centerline average roughness Ra of single fiber surface, strand strength and breaking pressure of pressure vessel manufactured using the obtained carbon fiber bundle ) Was measured according to the above method. The measurement results are shown in Table 2.

Example 10
In the production of the carbon fiber precursor acrylic fiber bundle, the concentration and temperature of the dimethylacetamide aqueous solution, which is a coagulating liquid, are set to 68% by mass and 39 ° C, respectively, the nozzle pore size is set to 60 μm, and the tension applied to the coagulated yarn is controlled to 73 mgf / filament. Then, the same procedure as in Example 1 was carried out except that the stretching ratio in the air was 1.07 times and the stretching ratio in the stretching / washing tank was 2.50 times. The total draw ratio from taking the coagulated yarn to obtaining the drawn yarn after treatment in the hot water tank is 2.62 times, and the total draw ratio from taking the coagulated yarn to drawing in a pressurized saturated steam atmosphere is 9. It was .18 times.
Table 1 summarizes the spinning conditions for the carbon fiber precursor acrylic fiber bundle. The physical properties of the obtained carbon fiber precursor acrylic fiber bundle (major axis / minor axis of the single fiber, recessed distance / minor axis of the single fiber, and centerline average roughness Ra of the surface of the single fiber), and the obtained carbon fiber bundle. Physical properties (major axis / minor axis of single fiber, recess distance / minor axis of single fiber, centerline average roughness Ra of single fiber surface, strand strength and breaking pressure of pressure vessel manufactured using the obtained carbon fiber bundle ) Was measured according to the above method. The measurement results are shown in Table 2.

Example 11
In the production of the carbon fiber precursor acrylic fiber bundle, the concentration and temperature of the dimethylacetamide aqueous solution as the coagulating liquid were set to 66% by mass and 39 ° C., respectively, the tension applied to the coagulated yarn was controlled to 74 mgf / filament, and the draw ratio in the air. Was 1.04 times, and the stretching ratio under a pressurized saturated steam atmosphere was 3.40 times, but the same procedure as in Example 1 was carried out. The total draw ratio from taking the coagulated yarn to obtaining the drawn yarn after treatment in the hot water tank is 2.65 times, and the total draw ratio from taking the coagulated yarn to drawing in a pressurized saturated steam atmosphere is 9. It was 0.01 times.
Table 1 summarizes the spinning conditions for the carbon fiber precursor acrylic fiber bundle. The physical properties of the obtained carbon fiber precursor acrylic fiber bundle (major axis / minor axis of the single fiber, recessed distance / minor axis of the single fiber, and centerline average roughness Ra of the surface of the single fiber), and the obtained carbon fiber bundle. Physical properties (major axis / minor axis of single fiber, recess distance / minor axis of single fiber, centerline average roughness Ra of single fiber surface, strand strength and breaking pressure of pressure vessel manufactured using the obtained carbon fiber bundle ) Was measured according to the above method. The measurement results are shown in Table 2.

Comparative Example 11
In the production of the carbon fiber precursor acrylic fiber bundle, the temperature of the dimethylacetamide aqueous solution, which is a coagulating liquid, is set to 30 ° C., the tension applied to the coagulated yarn is controlled to 60 mgf / filament, and the draw ratio under a pressurized saturated steam atmosphere is 4. It was carried out in the same manner as in Example 1 except that it was multiplied by 20. The total draw ratio from taking the coagulated yarn to obtaining the drawn yarn after treatment in the hot water tank is 2.57 times, and the total draw ratio from taking the coagulated yarn to drawing in a pressurized saturated steam atmosphere is 10. It was 0.8 times.
Table 1 summarizes the spinning conditions for the carbon fiber precursor acrylic fiber bundle. The physical properties of the obtained carbon fiber precursor acrylic fiber bundle (major axis / minor axis of the single fiber, recessed distance / minor axis of the single fiber, and centerline average roughness Ra of the surface of the single fiber), and the obtained carbon fiber bundle. Physical properties (major axis / minor axis of single fiber, recess distance / minor axis of single fiber, centerline average roughness Ra of single fiber surface, strand strength and breaking pressure of pressure vessel manufactured using the obtained carbon fiber bundle ) Was measured according to the above method. The measurement results are shown in Table 2.
The major axis / minor axis of the carbon fiber precursor acrylic fiber bundle and the single fiber of the carbon fiber bundle are almost the same (slightly increased) as in Example 1, but the dent distance / minor axis of the single fiber and the centerline average roughness of the single fiber surface are coarse. Ra increased as compared with Example 1. The strand strength of the carbon fiber bundle was 5600 MPa, and the breaking pressure of the pressure vessel was 123 MPa, which were lower than those of Example 1.

Comparative Example 12
In the production of carbon fiber precursor acrylic fiber bundles, the temperature of the dimethylacetamide aqueous solution, which is a coagulating liquid, is set to 30 ° C., the tension applied to the coagulated yarn is controlled to 60 mgf / filament, and the draw ratio in the drawing / washing tank is 2.50. The same procedure as in Example 1 was carried out except that the stretching ratio was set to 4.20 times in a pressurized saturated steam atmosphere. The total draw ratio from taking the coagulated yarn to obtaining the drawn yarn after treatment in the hot water tank is 2.47 times, and the total draw ratio from taking the coagulated yarn to drawing in a pressurized saturated steam atmosphere is 10. It was quadruple.
Table 1 summarizes the spinning conditions for the carbon fiber precursor acrylic fiber bundle. The physical properties of the obtained carbon fiber precursor acrylic fiber bundle (major axis / minor axis of the single fiber, recessed distance / minor axis of the single fiber, and centerline average roughness Ra of the surface of the single fiber), and the obtained carbon fiber bundle. Physical properties (major axis / minor axis of single fiber, recess distance / minor axis of single fiber, centerline average roughness Ra of single fiber surface, strand strength and breaking pressure of pressure vessel manufactured using the obtained carbon fiber bundle ) Was measured according to the above method. The measurement results are shown in Table 2.
The major axis / minor axis of the carbon fiber precursor acrylic fiber bundle and the single fiber of the carbon fiber bundle are almost the same (slightly increased) as in Example 1, but the dent distance / minor axis of the single fiber and the centerline average roughness of the single fiber surface are coarse. Ra increased as compared with Example 1. The strand strength of the carbon fiber bundle was 5700 MPa, and the breaking pressure of the pressure vessel was 124 MPa, which were lower than those of Example 1.

Comparative Example 13
In the production of the carbon fiber precursor acrylic fiber bundle, the concentration of the dimethylacetamide aqueous solution, which is a coagulating liquid, is set to 65% by mass, the tension applied to the coagulated yarn is controlled to 95 mgf / filament, and stretching is performed without stretching in the air. The same procedure as in Example 1 was carried out except that the stretching ratio in the washing tank was 3.40 times and the stretching ratio in a pressurized saturated steam atmosphere was 2.00 times. The total draw ratio from taking the coagulated yarn to obtaining the drawn yarn after treatment in the hot water tank is 3.33 times, and the total draw ratio from taking the coagulated yarn to drawing in a pressurized saturated steam atmosphere is 6. It was .66 times.
Table 1 summarizes the spinning conditions for the carbon fiber precursor acrylic fiber bundle. The physical properties of the obtained carbon fiber precursor acrylic fiber bundle (major axis / minor axis of the single fiber, recessed distance / minor axis of the single fiber, and centerline average roughness Ra of the surface of the single fiber), and the obtained carbon fiber bundle. Physical properties (major axis / minor axis of single fiber, recess distance / minor axis of single fiber, centerline average roughness Ra of single fiber surface, strand strength and breaking pressure of pressure vessel manufactured using the obtained carbon fiber bundle ) Was measured according to the above method. The measurement results are shown in Table 2.
The major axis / minor axis of the carbon fiber precursor acrylic fiber bundle and the single fiber of the carbon fiber bundle and the recessed distance / minor axis of the single fiber are almost the same (slightly reduced) as in Example 1, but the centerline average roughness of the single fiber surface is rough. Ra increased as compared with Example 1. The strand strength of the carbon fiber bundle was 4400 MPa, and the breaking pressure of the pressure vessel was 85 MPa, which were lower than those of Example 1.

Comparative Example 14
In the production of carbon fiber precursor acrylic fiber bundles, the tension applied to the coagulated yarn is controlled to 65 mgf / filament, the draw ratio in the air is set to 1.20 times, and the draw ratio in the draw / washing tank is set to 3.60 times. The same procedure as in Example 1 was carried out except that the stretching ratio under a pressurized saturated steam atmosphere was 2.60 times. The total draw ratio from taking the coagulated yarn to obtaining the drawn yarn after treatment in the hot water tank is 4.23 times, and the total draw ratio from taking the coagulated yarn to drawing in a pressurized saturated steam atmosphere is 11. It was 0.0 times.
Table 1 summarizes the spinning conditions for the carbon fiber precursor acrylic fiber bundle. The physical properties of the obtained carbon fiber precursor acrylic fiber bundle (major axis / minor axis of the single fiber, recessed distance / minor axis of the single fiber, and centerline average roughness Ra of the surface of the single fiber), and the obtained carbon fiber bundle. Physical properties (major axis / minor axis of single fiber, recess distance / minor axis of single fiber, centerline average roughness Ra of single fiber surface, strand strength and breaking pressure of pressure vessel manufactured using the obtained carbon fiber bundle ) Was measured according to the above method. The measurement results are shown in Table 2.
The major axis / minor axis of the carbon fiber precursor acrylic fiber bundle and the single fiber of the carbon fiber bundle and the recessed distance / minor axis of the single fiber were lower than those in Example 1, and the centerline average roughness Ra of the single fiber surface was It was almost the same as in Example 1. The strand strength of the carbon fiber bundle was 5400 MPa, and the breaking pressure of the pressure vessel was 115 MPa, which were lower than those of Example 1.

Comparative Example 15
In the production of the carbon fiber precursor acrylic fiber bundle, the same procedure as in Example 1 was carried out except that the tension applied to the coagulated yarn was controlled to 45 mgf / filament and the draw ratio in a pressurized saturated steam atmosphere was set to 4.20 times. did. The total draw ratio from taking the coagulated yarn to obtaining the drawn yarn after treatment in the hot water tank is 2.57 times, and the total draw ratio from taking the coagulated yarn to drawing in a pressurized saturated steam atmosphere is 10. It was 0.8 times.
Table 1 summarizes the spinning conditions for the carbon fiber precursor acrylic fiber bundle. The physical properties of the obtained carbon fiber precursor acrylic fiber bundle (major axis / minor axis of the single fiber, recessed distance / minor axis of the single fiber, and centerline average roughness Ra of the surface of the single fiber), and the obtained carbon fiber bundle. Physical properties (major axis / minor axis of single fiber, recess distance / minor axis of single fiber, centerline average roughness Ra of single fiber surface, strand strength and breaking pressure of pressure vessel manufactured using the obtained carbon fiber bundle ) Was measured according to the above method. The measurement results are shown in Table 2.
The major axis / minor axis of the carbon fiber precursor acrylic fiber bundle and the single fiber of the carbon fiber bundle and the recessed distance / minor axis of the single fiber were almost the same as in Example 1, but the centerline average roughness Ra of the single fiber surface was almost the same. Was lower than that of Example 1. The strand strength of the carbon fiber bundle was 5500 MPa, and the breaking pressure of the pressure vessel was 123 MPa, which were lower than those of Example 1.

Comparative Example 16
In the production of the carbon fiber precursor acrylic fiber bundle, the same procedure as in Example 1 was carried out except that the tension applied to the coagulated yarn was controlled to 35 mgf / filament.
Table 1 summarizes the spinning conditions for the carbon fiber precursor acrylic fiber bundle. The physical properties of the obtained carbon fiber precursor acrylic fiber bundle (major axis / minor axis of the single fiber, recessed distance / minor axis of the single fiber, and centerline average roughness Ra of the surface of the single fiber), and the obtained carbon fiber bundle. Physical properties (major axis / minor axis of single fiber, recess distance / minor axis of single fiber, centerline average roughness Ra of single fiber surface, strand strength and breaking pressure of pressure vessel manufactured using the obtained carbon fiber bundle ) Was measured according to the above method. The measurement results are shown in Table 2.
The major axis / minor axis of the carbon fiber precursor acrylic fiber bundle and the single fiber of the carbon fiber bundle and the recessed distance / minor axis of the single fiber were almost the same as in Example 1, but the centerline average roughness Ra of the single fiber surface was almost the same. Was lower than that of Example 1. The strand strength of the carbon fiber bundle was 5700 MPa, which was lower than that of Example 1.

The carbon fiber precursor acrylic fiber of the present invention has a major axis / minor axis having a characteristic cross-sectional shape of a single fiber, and a carbon fiber having a similar major axis / minor axis cross-sectional shape can be obtained. Since the carbon fiber bundle made of this carbon fiber is excellent in impregnation with the resin composition, it is useful for obtaining a high-strength CFRP tank.

1: Cross section of single fiber
2: The circumscribed rectangle with the smallest area
3: A straight line that touches the cross section of a single fiber at two points
4. A point on the circumference of the region farthest from the straight line 3
X: major axis
Y: minor diameter
Z: dent distance

Claims (10)

A carbon fiber having a center line average roughness Ra of the surface of the single fiber of 6.0 nm or more and 13 nm or less, and a major axis / minor axis of the single fiber of 1.11 or more and 1.245 or less. The carbon fiber according to claim 1, wherein the recess distance / minor axis of the single fiber is 0.011 or more and 0.018 or less. The carbon fiber according to claim 1, wherein the center line average roughness Ra of the surface of the single fiber is 10 nm or less, and the major axis / minor axis of the single fiber is 1.135 or more. The carbon fiber according to claim 3, wherein the dent distance / minor axis of the single fiber is 0.0145 or more. A carbon fiber precursor acrylic fiber having a center line average roughness Ra of the surface of the single fiber of 18 nm or more and 27 nm or less, and a major axis / minor axis of the single fiber of 1.11 or more and 1.245 or less. The carbon fiber precursor acrylic fiber according to claim 5, wherein the recess distance / minor axis of the single fiber is 0.011 or more and 0.018 or less. The carbon fiber precursor acrylic fiber according to claim 5, wherein the center line average roughness Ra of the surface of the single fiber is 24 nm or less, and the major axis / minor axis of the single fiber is 1.135 or more. The carbon fiber precursor acrylic fiber according to claim 7, wherein the recess distance / minor axis of the single fiber is 0.0145 or more. A method for producing a carbon fiber precursor acrylic fiber bundle, which comprises the following steps 1) to 3) and satisfies the following conditions 4) and 5).
1) Acrylonitrile-based polymer solution is discharged from a spinneret to coagulate in a coagulation liquid having a coagulation liquid concentration of 65% by mass or more and 70% by mass or less and a coagulation liquid temperature of 36 ° C. or more and 40 ° C. or less. A step of obtaining a yarn and at the same time taking it while controlling the tension applied to the coagulated yarn to 55 mgf / filament or more and 75 mgf / filament or less.
2) After the coagulated yarn taken in the above 1) step is drawn in the air at 1.00 times or more and 1.15 times or less, using water at 50 ° C. or higher, from 4 steps or more and 7 steps or less. Stretching / washing is performed in a magnification range of 2.4 times or more and 2.7 times or less in a washing / stretching tank, and 0.97 times or more and 1.1 times or less in a hot water tank using water at 95 ° C. or higher. A step of obtaining a drawn yarn by relaxing or drawing the above.
3) A step of applying an oil agent to the drawn yarn after drawing in the step 2), drying the yarn, and then stretching the yarn to 3.0 times or more and 4.5 times or less in a pressurized steam atmosphere of 130 ° C. or higher and 160 ° C. or lower.
4) The total draw ratio of the coagulated yarn from the time when the coagulated yarn in the step 1) is taken from the coagulating liquid to the time when the drawn yarn in the step 2) is obtained is 2.4 times or more and 2.7 times or less.
5) The total draw ratio from the taking of the coagulated yarn in the step 1) to the drawing in the pressurized steam atmosphere of the step 3) is 9.0 times or more and 12 times or less. A method for producing a carbon fiber bundle, which comprises the following steps 7) to 9).
7) The carbon fiber precursor acrylic fiber bundle composed of the carbon fiber precursor acrylic fiber according to any one of claims 5 to 8 is heated to 200 ° C. or higher and 300 ° C. or lower in an oxidizing atmosphere to make it flame resistant. Flame resistant process for making fiber bundles.
8) A pre-carbonization step in which the flame-resistant fiber bundle is heated at 550 ° C. or higher and 800 ° C. or lower in a non-oxidizing atmosphere to form a pre-carbonized fiber bundle.
9) A high-temperature carbonization step in which the pre-carbonized fiber bundle is heated at 1200 ° C. or higher and 3000 ° C. or lower in a non-oxidizing atmosphere to form a carbon fiber bundle.

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